Polyvinyl chloride products have been gaining popularity increasingly in recent years, especially in the construction industry, in the packaging industry, and in the insulation of wires and cables.
Although PVC is inherently flame-resistant, the production of hydrochloric acid at high temperatures may cause secondary damage in fires, for example by rendering machinery useless by corrosion.
To prevent this production of HCl, attempts have been made to add hydrochloric acid binding chemicals which also serve as fillers, such as calcium carbonate, prior to fabrication. This has not been as successful as anticipated, since only part of the HCl is bound. The ground chalk commonly used as the filler has proven to be too coarsely dispersed, and is usually contained in quantities that are too small to chemically bind all of the HCl that may be developed.
An attempt has also been made to provide a larger reaction surface for binding the HCl by using highly disperse calcium carbonate produced by precipitation, with an average grain size of 250 m.mu., corresponding to a special surface area of 10 to 18 m.sup.2 /g (German "Offenlegungschrift" 1,926,412). Even then, however, an approximately quantitative binding of the hydrochloric acid is achieved only if the chalk is used in such a great quantity as to appreciably impair the physical characteristics of the compound. An almost complete binding of the volatile HCl is achieved only with 100 to 120 parts of CaCO.sub.3 per 100 parts of PVC, that is, with a very appreciable stoichiometric excess of CaCO.sub.3, but this detracts especially from the tensile strength of the maufactured products.